The present invention relates to an inductive position indicator especially for determination of an angular position of a throttle flap of an internal combustion engine.
More particularly, it relates to such an inductive position indicator which has an oscillator circuit and reversible oscillating circuit branches, as well as a position detecting element which cooperates with the oscillating circuit branches for position-dependent change of its inherent frequencies, and with an evaluating circuit which determines the position from the adjusting inherent frequencies.
In many fields of technology it is required to determine the position of a control member, such as for example a throttle flap or the like. For this purpose, inductive position indicators are used in which in dependence on the position a change in the inductance of at least one coil is adjusted. The respective inductance value is therefore a measurement for the position. When compared with a position determination by means of a potentiometer, this method provides for the advantage in that the inductive position indicator is less vulnerable to dirtying which can lead to contact problems and therefore to faulty measurements. Also, such an inductive position indicator has a lower wear due to its contact-free operational principle.
An inductive position indicator of the above mentioned general type is disclosed in U.S. Pat. No. 4,644,570. Here the position detecting element is formed as a differential transmitter. This means that two electric values change oppositely in dependence on the detected position. For this purpose two coils are provided and cooperate with a core in accordance with the eddy current principle, so that depending on the position it approaches correspondingly one of the coils and moves away from the other coil. The coils are connected alternatingly with a capacitor so that in one switching position a first oscillating circuit branch and in the other switching position a second oscillating circuit branch is formed. Both oscillating circuit branches are operated one after the other with an oscillator of an oscillator circuit, and due to the position-dependent inductance values, the associated inherent frequencies are adjusted. The disadvantage here is that the known inductive position indicator has a relatively low sensitivity and is further subjected to a non-linearity. Furthermore, during reversing of the oscillating circuit transient oscillations occur which distort the measurement results.